Nonpareil: Calculator Microassembler and Simulator

Screenshot

Screenshot showing two instances of Nonpareil running an HP-45 and
HP-55. The HP-45 is using a PNG image with transparency, so it has a
shaped window, while the HP-55 has a normal window. The HP-45 window
can be dragged by clicking it anywhere other than the keys, and it's
menus can be popped up with a right click.